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Views: 5,494

Identify the hydrogen-bond donors and acceptors in each of the four bases on page 4

Topic:

Chemistry

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Views: 5,674

For double-helix formation,

Δ G

can be measured to be

- 54 kJ mol^{- 1} (- 13 kcal

\mathrm{mol}^{-1}

) a t

\mathrm{pH} 7.0

in

1 \mathrm{M} \mathrm{NaCl}

a t

25^{\circ} \mathrm{C}(298 \mathrm{K}) .

T h e h e a t re l e a se d in d i c a t es an e n t ha lp yc han g eo f

-251 \mathrm{kJ} \mathrm{mol}^{-1}

\left(-60 \mathrm{kcal} \mathrm{mol}^{-1}\right) .$ For this process, calculate the entropy change for the system and the entropy change for the surroundings.

Topic:

Chemistry

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Views: 5,755

What is the pH of a 0.1 M solution of acetic

acid (p K_{a} = 4.75) ?

x

be the concentration of

H^{+}

ions released from acetic acid when it dissociates. The solutions to a quadratic equation of the form

a x^{2} + b x + c = 0

x = (- b \pm b^{2} - 4 a c) /2 a

Topic:

Chemistry

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Views: 5,048

What is the pH of a 0.1 M solution of ethylamine, given that the

p K_{a}

of ethylammonium ion

(CH_{3} CH_{2} NH_{3}^{+})

10.70 ?

Topic:

Chemistry

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Views: 5,904

A solution is prepared by adding 0.01 M acetic acid and

0.01 M

ethylamine to water and adjusting the

pH

7.4.

What is the ratio of acetate to acetic acid? What is the ratio of ethylamine to ethylammonium ion?

Topic:

Chemistry

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Views: 5,761

. You wish to prepare a buffer consisting of acetic acid and sodium acetate with a total acetic acid plus acetate concentration of

250 mM

5.0.

What concentrations of acetic acid and sodium acetate should you use? Assuming you wish to make 2 liters of this buffer, how many moles of acetic acid and sodium acetate will you need? How many grams of each will you need (molecular weights: acetic acid 60.05 g mol

^{- 1}

, sodium acetate,

82.03 g mol^{- 1}) ?

Topic:

Chemistry

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Views: 5,939

On average, estimate how many base differences there are between two human beings.

Topic:

Chemistry

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Views: 5,303

An enzyme that catalyzes disulfide-sulfhydryl exchange reactions, called protein disulfide isomerase (PDI), has been isolated. PDI rapidly converts inactive scrambled ribonuclease into enzymatically active ribonuclease. In contrast, insulin is rapidly inactivated by PDI. What does this important observation imply about the relation between the amino acid sequence of insulin and its three-dimensional structure?

Topic:

Chemistry

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Views: 5,458

The shape of hair is determined in part by the pattern of disulfide bonds in keratin, its major protein. How can curls be induced?

Topic:

Chemistry

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Question 10

Views: 5,864

Most proteins have hydrophilic exteriors and hydrophobic interiors. Would you expect this structure to apply to proteins embedded in the hydrophobic interior of a membrane? Explain.

Topic:

Chemistry

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Question 11

Views: 5,584

Proteins that span biological membranes often contain

α

helices. Given that the insides of membranes are highly hydrophobic (Section

12.2),

predict what type of amino acids would be in such an

α

helix. Why is an

α

helix particularly suited to existence in the hydrophobic environment of the interior of a membrane?

Topic:

Chemistry

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Question 12

Views: 5,487

α

β

subunits of hemoglobin bear a remarkable structural similarity to myoglobin. However, in the subunits of hemoglobin, certain residues that are hydrophilic in myoglobin are hydrophobic. Why might this be the case?

Topic:

Chemistry

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Question 13

Views: 5,411

Proteins are quite stable. The lifetime of a peptide bond in aqueous solution is nearly 1000 years. However, the free energy of hydrolysis of proteins is negative and quite large. How can you account for the stability of the peptide bond in light of the fact that hydrolysis releases much energy?

Topic:

Chemistry

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Question 14

Views: 5,901

For an amino acid such as alanine, the major species in solution at

pH

7 is the zwitterionic form. Assume a

p K_{a}

value of 8 for the amino group and a

p K_{a}

value of 3 for the carboxylic acid. Estimate the ratio of the concentration of the neutral amino acid species (with the carboxylic acid protonated and the amino group neutral) to that of the zwitterionic species at

pH 7

1.3)

Topic:

Chemistry

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Question 15

Views: 5,397

Translate the following amino acid sequence into one-letter code: Glu-Leu-Val-Ile-Ser-IleSer-Leu-Ile-Val-Ile-Asn-Gly-Ile-Asn-Leu-Ala-Ser-ValGlu-Gly-Ala-Ser.

Topic:

Chemistry

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Question 16

Views: 5,197

The only constant is change. Explain how two different cell types from the same organism will have identical genomes but may have vastly divergent proteomes.

Topic:

Chemistry

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Question 17

Views: 5,406

It's in the bag. Suppose that you precipitate a protein with

1 M (NH_{4})_{2} SO_{4}

and that you wish to reduce the concentration of the

(NH_{4})_{2} SO_{4}

1 ml

of your sample and dialyze it in

1000 ml

of buffer. At the end of dialysis, what is the concentration of

(NH_{4})_{2} SO_{4}

in your sample? How could you further lower the

(NH_{4})_{2} SO_{4}

Topic:

Chemistry

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Question 18

Views: 5,304

Sedimenting spheres. What is the dependence of the sedimentation coefficient

s

of a spherical protein on its mass? How much more rapidly does an

80 -

kDa protein sediment than does a

40 -

Topic:

Chemistry

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Question 19

Views: 5,109

Size estimate. The relative electrophoretic mobilities of a 30 -kDa protein and a 92 -kDa protein used as standards on an SDS-polyacrylamide gel are 0.80 and

0.41,

respectively. What is the apparent mass of a protein having a mobility of 0.62 on this gel?

Topic:

Chemistry

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Question 20

Views: 5,311

Column choice. (a) The octapeptide AVGWRVKS was digested with the enzyme trypsin. Which method would be most appropriate for separating the products: ion-exchange or gel-filtration chromatography? Explain. (b) Suppose that the peptide was digested with chymotrypsin. What would be the optimal separation technique? Explain.

Topic:

Chemistry

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